Osteoporosis is one of the most common and serious of the age-related diseases. Primarily affecting women in their post menopausal years, it is responsible for more than 200,000 hip fractures annually. Approximately 24,000 of these patients die within 3 months of the fracture incident. Over 3 million others suffer considerable pain and debility as a result of wrist and spine fractures. Despite an intensive research effort, the cause of osteoporosis still eludes us and we do not yet have satisfactory cures. There are marked racial differences in the susceptibility to osteoporosis. Whites are highly susceptible to the disease, whereas blacks are almost totally immune. The reasons for these racial differences are not clearly understood and must hold important clues to the pathogenetic mechanism(s) underlying the disease. The popular explanation is that black people have a greater skeletal mass than whites, but the scientific basis for this belief is weak. While there are some data to support this conclusion, there is an equal amount of data which suggests that the opposite is the case. However, more importantly, bone mass is not the only, and may not even be the main determinant of bone strength. Surprisingly, there has not been one study in which bone structure has been compared amongst different racial groups. Neither have there been any attempts to study the effect of race on the mechanical properties of bone. The primary goal of this research project is to gain a clear understanding of why this racial difference exists by performing a correlative study of iliac crest and vertebral bone structure and strength as functions of age and sex in black versus white people. The bone structure will be assessed quantitatively using the well-established, powerful technique of bone histomorphometry. The mechanical properties of trabecular bone will be characterized using a materials testing system and will be related to the histomorphometrically-determined structural parameters. By combining these techniques, the proposed study will generate significant new information on the important and intriguing question of why whites are more susceptible to osteoporosis than blacks and, in addition, will provide valuable information on how representative the standard iliac biopsy site is of the axial skeleton both in terms of static histomorphometric measures and mechanical strength.